It is noteworthy that GPx-3 is a major peroxide scavenger in yeast, as deletion of this enzyme results in a UNC2250 dramatic increase in H2O2 sensitivity, contrary to deletion of the GPx-1 and GPx-2 isoforms. We noticed a discrepancy between the GPx protein level and its activity in trophoblasts exposed to FA. This could be due to variations in the intracellular availability of GPx cofactors. We have previously observed a similar discrepancy with SOD-1 protein Zidovudine expression and the intracellular SOD-1 cofactor concentration during trophoblast cell fusion. Recent publications describe a protective effect of selenium against FA-induced oxidative stress. However, more experiments are needed to quantify selenium during trophoblast differentiation and to confirm its protective effect against FA exposure of trophoblasts. It is interesting to note that catalase activity increased 72h after FA exposure, compared to 24h for GPx. This suggests that higher H2O2 concentrations are produced 72h after FA exposure, an effect responsible for the diminution of cell fusion. Indeed, it is known that catalase metabolizes higher levels of hydrogen peroxide than GPx, without consuming additional GSH. We found here that exogenous H2O2 decreased trophoblast fusion and differentiation. This is also supported by a study performed by Heazell and colleagues, who found that BeWo choriocarcinoma cells treated with H2O2 presented a decrease in cell fusion. All these results suggest that excessive reactive oxygen species are generated after FA exposure, inducing increased expression of antioxidant enzymes. This would be a compensatory mechanism for preventing cell damage, as observed in lung tissue after FA in halation. It is supported by the marked increase in ASCT2 gene and protein expression after 24h. ASCT2 enables cell uptake of alanine, serine, cysteine and glutamine, which are involved in GSH synthesis. It has been reported in other cell types that increased ASCT2 expression facilitates uptake of glutamine, which is deaminated to glutamate by the mitochondrial glutaminase isoform 1 or 2.